ansys shell elements
DESCRIPTION
Ansys Shell Elements LectureTRANSCRIPT
ME-380 Course Notes
ANSYS LESSON 4Symmetry and Shell Elements
David Herrin, Ph.D.University of Kentucky
ME-380 Course Notes
Solution Time
Plane Stress/Plane Strain/Symmetry
g Roughly proportional to the number of degrees of freedom in a model squared
g Doubling the nodes implies a four fold increase
cdN - )( DOF ×=
ME-380 Course Notes
Symmetry
Plane Stress/Plane Strain/Symmetry
g Many large structures possess some form of symmetry
Symmetry in geometrySymmetry in loading
g Easy way to reduce a model to a more manageable size
g Solution time can be reduced an order of magnitude
ME-380 Course Notes
Types of Symmetry
Plane Stress/Plane Strain/Symmetry
g Axisymmetrytypical cross-section
of coffee cup
ME-380 Course Notes
Types of Symmetry
Plane Stress/Plane Strain/Symmetry
g Reflective Symmetry
FX
Y
Z
Simply supported plate
Model only this section
ME-380 Course Notes
Reflective Symmetry
Plane Stress/Plane Strain/Symmetry
g Symmetric boundary conditions
X
Y
Z
0=θ=θ= yxzu
0=θ=θ= zyxu
0=θ=θ
===
zy
zyx uuu
4F
0=θ=θ
===
yx
zyx uuu
ME-380 Course Notes
Creating Areas and Using 2-D Elements
Symmetric Boundary Conditons
Degrees of Freedom
Plane X Y Z RX RY RZ
X = 0 0 F F F 0 0
Y = 0 F 0 F 0 F 0
Z = 0 F F 0 0 0 F
F = Free0 = Zero Displacement
ME-380 Course Notes
Creating Areas and Using 2-D Elements
Anti-Symmetric Boundary Conditons
Degrees of Freedom
Plane X Y Z RX RY RZ
X = 0 F 0 0 0 F F
Y = 0 0 F 0 F 0 F
Z = 0 0 0 F F F 0
F = Free0 = Zero Displacement
ME-380 Course Notes
Example - Reflective Symmetry
Plane Stress/Plane Strain/Symmetry
FixedRing
ME-380 Course NotesME-406 Course Notes
Checking Results
In-Class Exercise
3 in.
6 in.
1 in.
1 in.
ME-380 Course NotesME-406 Course Notes
Checking Results
g Add a Plane82 element typeOption - with thickness
Determining Strain Energy in ANSYS
g Set the thickness to be 0.25 inches
g Set the material properties to steelE = 30E6Nu = 0.3
ME-380 Course NotesME-406 Course Notes
Checking Results
Boundary Conditions
Symm B.C.
Symm B.C.200 lb/in
200 lb/in
ME-380 Course NotesME-406 Course Notes
Checking Results
g Establish the density controls along lines
Create a Mapped Mesh
g Solve the load set
g Setup an element table for strain energy and calculate the total strain energy
ME-380 Course Notes
Shell Elements
g Several shell element formulationsClassical shell theoryIsoparametricHybrid
Shell Elements
g Each formulation gives slightly different results
g Generally, triangular elements yield very good results
ME-380 Course Notes
SHELL63 - Four Node Quadrilateral
Shell Elements
g Element supports both in-plane and normal loads
g 6 DOF per node3 translations3 rotations
ME-380 Course Notes
SHELL63 - Four Node Quadrilateral
Shell Elements
g Thickness can vary across the element
g Pressures applied to the element surfaces have units of Force/Area
g Pressures applied to edges have units of Force/Unit Length
ME-380 Course Notes
SHELL93 - Eight Node Quadrilateral
Shell Elements
g Better suited for modeling curved shells
g 6 DOF per node3 translations3 rotations
ME-380 Course Notes
Modeling Guidlines
Shell Elements
g Flat shells
g Thickness to span ratios
1.0 and ≤bt
at
ab
ME-380 Course Notes
Modeling Guidlines
Shell Elements
g Curved shells
g Thickness to radius ratio
1.0 ≤rh
r
g Stress in the Z, or thickness, direction is zero
ME-380 Course Notes
Modeling Guidlines
Shell Elements
g Stress averaging at nodes (as used in contour plotting) can be invalid if the unit normal vectors differ by more than 5 degrees
g Parabolic shells are more cost effective
ME-380 Course Notes
Shell Elements
Shell Element Example
E = 10E6 psit = 0.25 in
ν = .3
Fixed on Rim
Y
X
Symmetric about XZ and YZ Planes
Uniform 100 psiPressure Load
ME-380 Course Notes
Add Shell Element Type and Constants
g Add the shell element type8 node elasticSHELL93
Shell Elements
g Set the real constants for the element typeTK(I) = 0.25
g Set material constants for aluminum
ME-380 Course Notes
Create Keypoints for Geometry
g Enter the following Keypoint locationsNPT = 1: x=0, y=0, z=0 NPT = 2: x=6, y=0, z=0NPT = 3: x=0, y=6, z=0NPT = 4: x=2, y=1, z=0NPT = 5: x=4, y=1, z=0NPT = 6: x=1, y=2, z=0NPT = 7: x=1, y=4, z=0
Shell Elements
ME-380 Course Notes
Create Lines and Arcs
g Create Lines betweenKP 1 and 2KP 1 and 3KP 4 and 5KP 6 and 7
g Create arcs betweenKP 2 and 3KP 4 and 6KP 5 and 7
Shell Elements
ME-380 Course Notes
Create and Mesh the Areas
Shell Elements
g Create areasArea #1 is the outer areaArea #2 is the inner hole areaPerform Boolean subtraction subtracting Area #2
from Area #1 to form Area #3g Set the mesh controls to an edge length of 0.2”
g Map area #3 using a free mesh
ME-380 Course Notes
Shell Elements
Apply Boundary Conditions
g Apply Boundary ConditionsSymmetry displacement constraints on lines
#1 and #2All degrees of freedom fixed on outer arcPressure of 100 psi applied to area #3
g Solve the load set
ME-380 Course Notes
Shell Elements
Postprocessing
View the deformed shape
View contour plots of the nodal displacements in all 6 DOF directions
View contour plot of the stressesNormal stress in x and y directionsShear stresses - XY, YZ, and XZVon Mises